Hi Prafulla,
Le 05/10/2010 07:57, Prafulla Wadaskar a écrit :
-----Original Message----- From: u-boot-bounces@lists.denx.de [mailto:u-boot-bounces@lists.denx.de] On Behalf Of Albert Aribaud Sent: Tuesday, October 05, 2010 3:52 AM To: u-boot@lists.denx.de Subject: [U-Boot] [PATCH] orion5x: optimize window size computation
Signed-off-by: Chris Mooremoore@free.fr
This is a simple optimization of the orion5x window size computation. This code was contributed by Chris Moore so I put his Signed-off-by rather than mine.
This is wrong, you should be singed-off since you are posting and Chris can be contributor Or let him post the patch.
I asked Albert to post the patch as I am mainly a U-Boot lurker and I have no U-Boot git tree. If there is a problem I don't mind if he signs off either with or without me.
Seehttp://www.mail-archive.com/u-boot@lists.denx.de/msg37075.html
arch/arm/cpu/arm926ejs/orion5x/cpu.c | 30 ++++++++++++++++++++---------- 1 files changed, 20 insertions(+), 10 deletions(-)
diff --git a/arch/arm/cpu/arm926ejs/orion5x/cpu.c b/arch/arm/cpu/arm926ejs/orion5x/cpu.c index c36d7bf..5c443fe 100644 --- a/arch/arm/cpu/arm926ejs/orion5x/cpu.c +++ b/arch/arm/cpu/arm926ejs/orion5x/cpu.c @@ -48,24 +48,34 @@ void reset_cpu(unsigned long ignored) }
/*
- Window Size
- Compute Window Size field value from size expressed in bytes
- Used with the Base register to set the address window
size and location.
- Must be programmed from LSB to MSB as sequence of ones followed by
- sequence of zeros. The number of ones specifies the size
of the window in
- 64 KByte granularity (e.g., a value of 0x00FF specifies
256 = 16 MByte).
- NOTE: A value of 0x0 specifies 64-KByte size.
- NOTES:
- A sizeval equal to 0x0 specifies 4 TB.
*/ unsigned int orion5x_winctrl_calcsize(unsigned int sizeval) {
- A return value of 0x0 specifies 64 KB.
- int i;
- unsigned int j = 0;
- u32 val = sizeval>> 1;
- /*
* Calculate the number of 64 KiB blocks needed minusone (rounding up).
* For sizeval> 0 this is equivalent to:* sizeval = (u32) ceil((double) sizeval / 65536.0) - 1*/- sizeval = (sizeval - 1)>> 16;
- for (i = 0; val>= 0x10000; i++) {
j |= (1<< i);val = val>> 1;- }
- return 0x0000ffff& j;
- /*
* Propagate 'one' bits to the right by 'oring' them.* We need only treat bits 15-0.*/- sizeval |= sizeval>> 1; /* 'Or' bit 15 onto bit 14 */
- sizeval |= sizeval>> 2; /* 'Or' bits 15-14 onto bits 13-12 */
- sizeval |= sizeval>> 4; /* 'Or' bits 15-12 onto bits 11-8 */
- sizeval |= sizeval>> 8; /* 'Or' bits 15-8 onto bits 7-0*/
- return sizeval;
BTW: How much this saves on size?
It is not so much a question of size. I am afraid that the other version was just plain *wrong* :( See my previous post here: http://www.mail-archive.com/u-boot@lists.denx.de/msg36996.html In this post I presented two versions: a) a corrected version along the lines of the original, b) a version similar to the above.
The loop version may be slightly shorter in code size, particularly if one removes the unnecessary and with 0x0000ffff at the end. But aesthetically I find the version above much more pleasing. (Didn't Donald Knuth write "The *Art* of Computer Programming"?) It is also much faster for large window sizes but this probably doesn't matter here.
Cheers, Chris